IMPACT OF LOW RATES OF NITROGEN APPLIED AT PLANTING ON SOYBEAN NITROGEN FIXATION

Abstract

Environmental conditions in the northern Great Plains can delay emergence, nitrogen (N) fixation and growth of soybean due to cool and wet soil conditions at planting. The objective was to evaluate the impact of low rates of N applied at planting on soybean N fixation and crop growth. A field experiment was established within corn soybean rotation using a split-plot design with four replications. Whole plots were no-tillage and conventional tillage and split plots were starter fertilizer. Nitrogen sources were ammonium nitrate or urea applied at four rates. The amount of plant N fixation increased with growth stage reaching a maximum fixation at the R5 growth stages. Plant ureide content decrease with increase N applied for all growth stages except R7. The increase in plant biomass contributed to an overall increase in yield indicating that in unfavorable environments application of N at planting can have a positive impact on soybean growth.

Keywords:

• soybean
• nitrogen
• soil fertility

ACKNOWLEDGMENTS

The authors thank Kurt Dagel, Dave Schneider and Max Pravecek for careful management of research plots, data collection and analysis for this study. USDA offers its programs to all eligible persons regardless of race, color, age, sex or national origin. Mention of trade name or commercial products in this publication is solely for the purpose for providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

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Notes

^†Conventional tillage treatment.

^‡Performed the previous fall.